This invention relates to a method and device for recording information on an information recording medium built up of a photoelectric sensor and a liquid crystal layer at a preset optimum applied voltage, and a method for measuring the transmittance of a liquid crystal recording medium which is applied to recording information.
So far, an arrangement wherein a polymer dispersion type of liquid crystal recording medium--in which a liquid crystal layer having liquid crystals dispersed and fixed in resin is formed on an electrode--is located in opposition to a photoelectric sensor having a photoconductive layer formed on an electrode layer has been known so as to record images by exposure to light at an applied voltage.
A typical construction of an image recorder used with such a polymer dispersion type of liquid crystal recording medium is illustrated in FIG. 1, in which reference numerals 10 and 20 stand for a photoelectric sensor and a liquid crystal recording medium, respectively. In the photoelectric sensor 10 a transparent electrode 12 and a photoconductive layer 13 are successively coated or otherwise formed on a transparent supporting substrate 11, and in the liquid crystal recording medium 20 a transparent electrode 22 and a polymer dispersion type of liquid crystal layer 23 are successively formed on a transparent supporting substrate 21. The photoconductive layer 13 used, for instance, may have a single-layer structure in which trinitrofluorenone is added to amorphous selenium or amorphous silicon for an inorganic photoconductive layer or to polyvinylcarbazole for an organic photoconductive layer, a formed structure in which a carrier generation layer obtained by dispersing an azo type pigment in a resin such as polyvinyl butyral is formed on a carrier transport layer obtained by mixing a hydrazone derivative with a resin such as polycarbonate, or other structures.
An arrangement in which, as shown in FIG. 1, a photoelectric sensor is opposed to a liquid crystal recording medium for exposure to light at an applied voltage, while a gap of about 10 .mu.m is maintained between them by a spacer of polyethylene, polyimide or other polymer, and an arrangement in which, as shown in FIGS. 2(a) and 2(b), a photoelectric sensor and a liquid crystal recording medium are stacked together, have been put forward in the art. The stacked form of recording medium is broken down into two types, one in which a liquid crystal recording layer is stacked directly on a photoelectric sensor, as shown in FIG. 2(a), and the other in which an middle layer 24 of a transparent dielectric material is interposed between them, as shown in FIG. 2(b).
When such an arrangement built up of the photoelectric sensor 10 and the liquid crystal recording medium 20 located in opposition thereto is irradiated with visible write light, while voltage is applied between both the electrodes 12 and 22 by a power source 30, the conductivity of the photoconductive layer 13 changes depending on the intensity of the light, resulting in a change in the electric field applied on the liquid crystal layer 23 and so a change in the orientation of the liquid crystal layer. This orientation, even when the applied voltage is put off for removal of the electric field, is maintained so that images can be recorded.
The thus recorded image information can be read by irradiating the liquid crystal recording medium 20 with read light from a light source 40 and reading the transmitted light with a photoelectric conversion element 60 to convert it to electrical signals, as shown in FIG. 4 by way of example. For the light source 40 a white light source such as a xenon or halogen lamp or a laser light source may be used. For the read light with which the liquid crystal recording medium is irradiated, it is preferable to select light of suitable wavelength by a filter 50. The incident light is modulated by the orientation of the liquid crystal layer of the liquid crystal recording medium, and the transmitted light is converted to electrical signals through the photoelectric conversion element 60 made up of diodes, etc. The resulting electrical signals may be processed by a printer or otherwise displayed on a CRT, if required.
The orientation of the liquid crystal layer of a liquid crystal recording medium depends on the magnitude of an applied voltage, the duration of an applied voltage, etc., and for recording images of a high contrast it is required to measure the degree of orientation of the liquid crystal layer. The degree of orientation of the liquid crystal layer may be found by monitoring the transmittance.
One typical method for measuring the transmittance is illustrated in FIG. 5. As illustrated, a photoelectric sensor 10 having a transparent electrode 12 and a photoconductive layer 13 successively formed on a transparent supporting substrate 11 and a liquid crystal medium 20 having a transparent electrode 22 and a liquid crystal layer 23 successively formed on a transparent supporting substrate 21 are opposed to each other with an air gap of about 10 .mu.m between them. At the same time as the supporting substrate of the photoelectric sensor 10 is irradiated with white light, voltage is applied by a power source 30 between the electrodes 12 and 22 with such a polarity that the electrode 12 becomes positive. As illustrated, black paper 43 is put on the surface of the supporting substrate of the photoelectric sensor 10, so that half the photoelectric sensor can be shielded light. Two sets of infrared light-emitting LEDs 41 and photoelectric conversion elements 42 are located on the side of the supporting substrate of the liquid crystal medium 20 in such a way that infrared light from the LEDs passes through the liquid crystal medium, and is then reflected by the surface of the photoconductive layer of the photoelectric sensor so that it can be incident on the photoelectric conversion elements. One set is located at the (light) portion of the photoelectric sensor that is irradiated with light and another is positioned at the (dark) portion of the photoelectric sensor that is shielded from light. As the transmittance of the liquid crystal medium increases upon the application of voltage, there is an increase in the quantity of the light incident on the photoelectric conversion elements 42, the output signals of which are monitored on an oscilloscope 65. A shutter 52 is located between the photoelectric sensor 10 and the light source. This shutter is in synchronism with the power source, and is preset such that it is put down simultaneously with the application of voltage and is put up after the lapse of 1/30 sec (33 msec). The signals of the photoelectric conversion element are monitored on the oscilloscope simultaneously with the application of voltage.
However, this conventional method for measuring the transmittance of a liquid crystal recording medium has a grave problem, because this is designed to detect the light that passes through the liquid crystal recording medium, and is reflected by the surface of the photoelectric sensor; no satisfactory detection signal can be obtained, because the surface reflectivity of the photoelectric sensor is low, and because infrared light is used as monitoring light so as to prevent the sensitization of the photoelectric sensor, and this places some limitation upon the usable wavelength region.
The magnitude, duration, etc., of the voltage applied on the liquid crystal layer may be preset by monitoring the transmittance of the liquid crystal layer. A problem with this method, however, is that an additional function of measuring the transmittance must be added to the information recorder, resulting in an increase in recorder size. Another problem is that the transmittance of the liquid crystal recording layer, because of depending largely on the wavelength of the monitoring light, must be corrected.
Still another problem with image recording according to such a method is that the recorded image becomes too light or too dark due to a slight difference in the magnitude and duration of an applied voltage, and this is true of even when the photoelectric sensor and liquid crystal recording medium having the same characteristics are used. Thus, it is very difficult to determine the conditions for recording images desired for those who record them, because the properties of the image recorded vary considerably depending on the magnitude and duration of an applied voltage.